Stormwater Assessment Glossary of Terms

Ad Valorem
A tax which is based on the value of the property.

Basin
A hydrologic unit consisting of a drainage system including a stream or body of impounded surface water plus all tributaries.

Basin Master Plan
A comprehensive study of the physical characteristics of a drainage basin. A master plan identifies flooding and water quality problems (or level of service deficiencies) and recommends solutions through a stormwater improvement program.

Best Management Practices (BMPs)
Activities or structural improvements that help reduce the volume of stormwater and improve the quality of stormwater runoff. BMPs include treatment requirements, operating procedures, and practices to control site runoff, spillage or leaks, sludge or waste disposal or drainage from raw material storage.

Billing Unit (BU)
The Sarasota County Stormwater Environmental Utility currently assesses its customers based on Stormwater Billing Units (BUs) which means 500 square feet of Impervious Area, which shall be used to calculate the number of BUs attributable to each Tax Parcel of Developed Property

Bioretention
A water quality practice that utilizes landscaping and soils to treat urban stormwater runoff by collecting it in shallow depressions. It then filters the runoff through a fabricated planting soil media.

Capital Improvement Program (CIP) 
A schedule of large-scale projects to improve stormwater level of service deficiencies identified in the Basin Master Plan.

Capital Improvement Assessment
In order to fund capital improvement projects, as identified in the Basin Master Plans, an assessment is levied on parcels in basins where capital projects are to be constructed. This Capital Improvement assessment is in addition to the annual Stormwater Service Assessment. Capital improvement assessments collected in a particular basin are used exclusively to fund capital projects within that basin. Basin Master Plans analyze the need for capital improvements in relation to established levels of service – structure flooding, street flooding, and water quality. Capital improvement assessments are calculated based on the project cost associated with a specified level of service and any related debt or financing cost and the total BUs of the parcels within the improvement area. The capital assessment is levied according to the BU count of a given parcel. Because the number and cost of projects varies in each basin, capital assessments vary between the basins.

Culvert
A short, closed (covered) conduit or pipe that passes stormwater runoff under an embankment, usually a roadway.

CWA
The Clean Water Act.

Detention facility or pond
A facility that collects water from developed areas and releases it at a slower rate than it enters the collection system. The excess of inflow over outflow is temporarily stored in a pond or a vault and is typically released over a few hours or a few days.

Direct Discharge
Unretained discharge from a proposed project to major receiving waters.

Drainage Basin (or watershed)
A geographic area which drains into a major body of water (for example a creek or bayou). The size and shape of a drainage basin is determined by the elevation of the land (topography). There are 27 drainage basins in Sarasota County.

EPA
Environmental Protection Agency.

Fiscal Year
The Stormwater Environmental Utility Fiscal Year is the period commencing on October 1 of each year and continuing through the next succeeding Sept. 30 (Example: November 2025 tax bills are for the fiscal year 2026, which runs October 1, 2025, to September 30, 2026.)

Flood
A temporary rise in flow or stage of any watercourse or stormwater conveyance system that results in stormwater runoff exceeding its normal flow boundaries and inundating adjacent, normally dry areas.

Flood Control
The specific regulations and practices that reduce or prevent the damage caused by stormwater runoff.

Floodplain
Any low-lying area of land adjacent to a waterbody that is subject to flooding.

Hydrologic Cycle
The circuit of water movement from the atmosphere to the earth and return to the atmosphere through various stages or processes such as precipitation, interception, runoff, infiltration, percolation, storage, evaporation, and transpiration.

Impervious Area
Hard surfaced areas which either prevent or severely restrict the entry of water into the soil mantle and/or cause water to run off the surface in greater quantities or at an increased rate of flow from that present under natural conditions prior to development. Common impervious surfaces include, but are not limited to, roof tops, sidewalks, walkways, patio areas, driveways, roadways, parking lots, storage areas and other surfaces which similarly affect the natural infiltration or runoff patterns which existed prior to development.

Invert
Elevation at the inside bottom of the pipe.

Non-Ad Valorem
An assessment that is not based on the value of the property. Factors such as contribution to the drainage system are used to determine stormwater non-ad valorem assessments; sometimes called a “user-fee”. 

Nonpoint Source Pollution (NPS)
Pollution that, unlike pollution from industrial and sewage treatment plants, comes from many diffuse sources. NPS pollution is caused by rainfall or snowmelt moving over and through the ground. As the runoff moves, it picks up and carries away natural and manmade pollutants, finally depositing them into lakes, rivers, wetlands, coastal waters, and even our underground sources of drinking water. Loadings of pollutants from NPS enter water bodies via sheet flow, rather than through a pipe, ditch, or other conveyance.

NPDES
National Pollutant Discharge Elimination System. The part of the Clean Water Act which requires permits for point source discharges. These permits, referred to as NPDES permits, are administered by the Florida Department of Environmental Protection.

Outfall
The point where runoff discharges from a sewer pipe, ditch, or other conveyance to a receiving body of water.

Pervious Area
Pervious area is the surface area, which, under standard conditions, is permeable to stormwater runoff and other surface water.

Point Source Pollution
Pollution from discrete conveyances, such as pipes or manmade ditches that discharge pollutants into waters of the United States. This includes not only discharges from municipal sewage plants and industrial facilities, but also collected storm drainage from larger urban areas, certain animal feedlots and fish farms, some types of ships, tank trucks, offshore oil platforms, and collected runoff from many construction sites.

Retention Ponds
Commonly used facilities that both remove pollutants from stormwater runoff and store floodwaters. A process that halts the downstream progress of stormwater runoff. This is typically accomplished using total containment involving the creation of storage areas that use infiltration devices, such as dry wells, to dispose of stored stormwater via percolation over a specified period. (As opposed to a more common detention pond.)

Runoff
Water originating from rainfall and other precipitation that ultimately flows into drainage facilities, rivers, streams, springs, seeps, ponds, lakes, and wetlands as well as shallow groundwater.

SEUAC
Ordinance No. 94-066 established the Stormwater Environmental Utility Advisory Committee (SEUAC). Comprised of ten residents of the stormwater utility area, SEUAC members are appointed by the Board of County Commissioners. The primary responsibility of the SEUAC is oversight of the utility’s programs, policies, and expenditures. The SEUAC makes recommendations to the Board, based on material and discussions presented at bi-monthly meetings.

Storm Drain
An opening, generally in the curb line, leading to an underground pipe or an open ditch carrying surface runoff. These lead directly to streams and do not go through a treatment or processing plant.

Stormwater
Precipitation from a storm event that flows into streams or accumulates in natural or constructed storage systems. Stormwater often includes pollutants and sediment from land surfaces.

Stormwater Facilities
Systems such as watercourses, constructed channels, storm drains, culverts, and detention/retention facilities that are used for the conveyance and/or storage of stormwater runoff.

Stormwater Level of Service (LOS)
The level of flooding which is considered acceptable for a given rain event. Sarasota County’s established level of service prohibits structure flooding and flooding of evacuation routes in a 100-year (1 percent chance) storm event. Flooding of neighborhood streets to a depth of 12 inches at the centerline of the road is allowed in a 100-year storm event.

Stormwater Management
Functions associated with planning, designing, constructing, maintaining, financing, and regulating the facilities (both constructed and natural) that collect, store, control and/or convey stormwater.

Stormwater System 
The entire assemblage of stormwater facilities located within a watershed.

Stormwater Utility Area
The unincorporated area of Sarasota County and the incorporated area in the city of Sarasota.

Surface Water
Water that remains on the surface of the ground, including rivers, lakes, reservoirs, streams, wetlands, impoundments, seas, estuaries, etc.

Swale
A shallow drainage conveyance with relatively gentle side slopes, generally with flow depths less than one foot. Often lined with grass and used as a conveyance for stormwater.

Total Maximum Daily Load (TMDL)
The maximum loading of a pollutant which can be released into a water body without adversely affecting water quality.

Watershed
A geographic area in which water, sediments, and dissolved materials drain to a common outlet, typically a point on a larger stream, a lake, an underlying aquifer, an estuary, or an ocean. A watershed is also sometimes referred to as the "drainage basin" of the receiving water body.

Wetland
An area inundated or saturated by ground or surface water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil condition.